Electrode positioning and position maintenance is a problem in many body stimulation contexts. Electrode position has been maintained through the use of sutures and electrode configurations which penetrate the body tissue itself. In addition, projections or tines have been employed to engage the body tissue to maintain the electrode in position. However, in some stimulation contexts, including temporary stimulation, such mechanical position maintenance devices are undesirable. For example, in the temporary stimulation context, such devices hinder the removal of the stimulation delivering lead. Electrode positioning, and electrode position maintenance, have also been accomplished by forming the lead body in various configurations.
One system by which a particular configuration may be established in a body stimulation lead is disclosed in U.S. Pat. No. 3,890,977, issued June 24, 1975 to Bruce C. Wilson for Kinetic Memory Electrodes, Catheters and Cannulae. In accordance with the Wilson disclosure, a lead may incorporate a material having a heat-activated mechanical memory. The desired configuration is established and the material annealed at high temperature. As the material cools to a temperature below its transitional temperature, it is reformed into a shape selected for ease of insertion. With the lead located at the desired position, the material having a mechanical memory is heated above its transitional temperature thereby returning it to its annealed shape. In this manner, a lead in accordance with the Wilson teaching can be configured for ease of insertion and reconfigured for anchoring or proper positioning of the lead electrode. However, at least at temperatures below the transitional temperature, the Wilson structure is not resilient as evidenced by its ability to be reformed for ease of insertion.
Another system whereby a desired configuration may be established in a body stimulation lead is disclosed in U.S. Pat. No. 3,729,008, issued Apr. 24, 1973 to Barough V. Berkovits for ELECTRODE FOR ATRIAL PACING WITH CURVED END FOR ATRIAL WALL ENGAGEMENT. In accordance with the Berkovits teaching, a portion of the lead body is provided with a curved configuration and additional insulation is applied at the area of curvature to cause the lead to assume the desired shape. While this approach may be initially effective, most known materials which are suitable for insulation of a body implantable lead also have a tendency to creep which, in time, causes the lead to depart from the desired configuration thus affecting the ability of the lead to retain the electrode in the desired position. The additional insulation also increases the bulk of the lead.
An additional system which facilitates the positioning of an electrode is disclosed in U.S. Pat. No. 3,516,412, issued June 23, 1970 to B. Ackerman for Bipolar Electrode Having Irregularity at Inserting End Thereof and Method of Insertion. The Ackerman system employs a lead having an electrode at its distal end with a second electrode being coiled around the lead through the entirety of its length. The coiled electrode provides a "linear irregularity" close to the distal electrode which irregularity provides an indication that the lead has been inserted a sufficient distance through a needle. The "linear irregularity" also assists in positioning the electrode. However, so as to maintain a flexibility throughout the lead, the material forming the coiled second electrode is extremely flexible which limits the force which may be applied by the irregularity to maintain the electrode in position.